OCR Text |
Show development and utilization of the greater portion of these ground-water reserves involves many" factors. Among the problems encountered are: water of poor quality; deterioration of quality with depth, or with recir- culation of used water; low yields from wells in some of the aquifers; remoteness of new aquifers from areas where excessive pumping has caused land subsidence; the limited period during which a large overdraft can be maintained; and, the legal rights of overlying land owners. Many of these problems have not yet been adequately evaluated and should be given top priority in future studies. The Region* s present ground-water overdraft will increase consider- ably by 1990, the earliest probable date that an importation program could be in effect. In the meantime, as the ground-water level declines, the price of pumped water will increase. Under such a competitive situ- ation, water utilization will tend to shift toward uses offering the highest economic return, unless constrained by legal and institutional factors. Some ground-water overdraft is expected to continue beyond year 2020, mostly in the Gila Subregion. This overdraft would occur largely as a result of agricultural development in the more remote ground-water basins; mineral developments, where surface supplies are unavailable; and water supply developments, in minor amounts, for the smaller com- munities remote from surface-water sources. It is not likely that ground-water overdraft would be entirely eliminated even in import water service areas where a combination surface-ground-import-water supply is utilized. The annual rate of ground-water overdraft after 2020 is largely conjectural. Figure 17 illustrates the regional water requirement and supply picture for 1965 through 2020. Water Quality The maintenance of an acceptable level of water quality is partic- ularly critical and complex in the Lower Colorado Region where maximum water utilization must be obtained by recycling available supplies. Colorado River water released to Mexico must continue to be regulated to closely approximate the quantities necessary to meet the Mexican Treaty commitment, while, at the same time, efforts must be continued to maintain quality. The high cost of imported water will probably dictate the continuation of an exceptionally high water-use efficiency with little or no allowance for transportation of salts or waste loads from the Region. A Colorado River Basin Salinity Improvement Program, coupled with an importation of high quality water to the Region, would stabilize the water quality of the Colorado River water near the present level. Negligible outflow from the Gila Subregion is expected to continue. The area having the most critical unmet need for water quality control 106 |